Physiology of dyspnea
- Richard M Schwartzstein, MD
Richard M Schwartzstein, MD
- Professor of Medicine
- Harvard Medical School
Breathing discomfort is one of the most common and distressing symptoms experienced by patients. While there are no symptom-specific data about the prevalence of this problem, the epidemiology of cardiac and pulmonary diseases indicates that the magnitude of the problem is large. Cardiac disease is the leading cause of death in the United States, and individuals with angina or myocardial infarction often experience breathlessness as the major (and sometimes sole) indicator that they are ill . In addition, asthma and chronic obstructive pulmonary disease (COPD) afflict approximately 34 million people in the United States, most of whom seek help from clinicians for relief of breathlessness [2,3].
Investigations of the language of dyspnea suggest that this symptom represents a number of qualitatively distinct sensations, and that the words utilized by patients to describe their breathing discomfort may provide insights into the underlying pathophysiology of the disease [4-7]. Furthermore, there is a growing recognition that one must distinguish between a "sensation" (the neural activation resulting from the stimulation of a receptor) and a "perception" (the reaction of the individual to that sensation) [8-10] and that healthcare providers are relatively poor at estimating the intensity of dyspnea by observing patients [11,12]. In addition, for a given intensity of a breathing sensation, the unpleasantness of the sensation may vary with the stimulus .
A consensus statement of the American Thoracic Society (ATS) has defined dyspnea as "a term used to characterize a subjective experience of breathing discomfort that is comprised of qualitatively distinct sensations that vary in intensity. The experience derives from interactions among multiple physiological, psychological, social, and environmental factors, and may induce secondary physiological and behavioral responses" .
The respiratory system is designed to maintain homeostasis with respect to gas exchange (adequate oxygenation) and the acid-base status of the organism (adjust arterial tension of carbon dioxide [PaCO2] to maintain normal pH). Derangements in oxygenation as well as acidemia lead to breathing discomfort. However, the development of dyspnea is a complex phenomenon which, in many patients, is the result of stimulation of a variety of mechanoreceptors throughout the upper airway, lungs, and chest wall, and which must also account for the sensations that arise when there is a mechanical load on the system (eg, increased airway resistance or decreased lung and/or chest wall compliance). The origins of dyspnea associated with the inadequate delivery of oxygen to, or utilization by, peripheral muscles are less well understood, but deserve consideration as well.
The ATS statement on the mechanisms, assessment, and management of dyspnea, as well as other ATS guidelines, can be accessed through the ATS web site at www.thoracic.org/statements.
Subscribers log in hereLiterature review current through: Sep 2017. | This topic last updated: Apr 22, 2016.References
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- INCREASED OUTPUT FROM THE RESPIRATORY CENTERS
- Acute hypercapnia
- Acute hypoxemia
- STIMULATION OF MECHANORECEPTORS
- Upper airway receptors
- Pulmonary receptors
- Chest wall receptors
- MECHANICAL LOADING OF THE RESPIRATORY SYSTEM
- NEUROMECHANICAL DISSOCIATION
- IMPAIRED OXYGEN DELIVERY OR UTILIZATION
- NEURAL ACTIVATION ASSOCIATED WITH BREATHING DISCOMFORT
- The affective dimension of dyspnea